Select the client(s) whose data that user needs access to, in the
Clients field (at the time of writing, it is the last field on
the page).

Click Save.

(Optional) Log into the Portal with users associated with clients, to
check that the expected data is accessible.

To force a sync with the newly added Portal, select the Portal from the
Portal list (Admin → Portals) in Canopy and click the Manually
synchronize portal toolbar button. All portals can also be manually
synced via the command line by running: